Step 1: Getting Started with Blender
Left Mouse Button (LMB) is generally in charge of moving stuff around
Middle Mouse Button (MMB) is what changes the viewpoint
Right Mouse Button (RMB) is what selects and deselects
A is select all / deselect all
E is Extrude
S is Scale
Space brings up a menu for item creation
So just press A until all of the items are pink then press Del then
Step 2: Make a Plane
Step 3: Subdivide
First enter Edit Mode
Then click Subdivide
The plane should now look like the picture.
If this doesn't work, make sure you have selected the plane by pressing A
Step 4: Give it the Shuriken Shape
To select a corner, make sure everything is deselected (selected points, or vertices, turn yellow)
RMB on the corner then drag it out and use LMB to set the vertex there.
Do this to all four sides.